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DescriptionThallus: foliose, often forming rosettes, small to medium sized, 2-3(-5) cm wide, deeply and broadly lobate; lobes: often crowded and imbricate, 0.5-1(-5) mm wide, thin (70-200 µm), rounded, flat or concave, often ascending and somewhat ear-shaped; margins: thin, entire or crenate; upper surface: smooth, dark green, olive or black, bright green in shaded habitats, occasionally pruinose; isidia: at first globose but soon scale-like, c. 0.15-0.3 mm wide, sometimes obscuring the thallus; lower surface: concolorous or paler, with white rhizines, sometimes forming ±scattered hapters; Apothecia: absent or common, appressed to sessile with slightly constricted base, 1-2(-2.5) mm broad; disc: plane, light to dark red-brown, smooth, epruinose or rarely pruinose; thalline margin: thin, granulose to lobulate, with primitive pseudocortex; true exciple: thin, subparaplectenchymatous to nearly euthyplectenchymatous; hymenium: hyaline, 130-170 µm tall; asci: narrowly clavate, 8-spored; ascospores: hyaline, ovoid to subellipsoid, with rounded ends, 4-celled or sometimes submuriform, (17-)26-34 x (8.5-)13-15(-18) µm; Pycnidia: marginal or laminal, ±immersed, pale; conidia: bacilliform, usually slightly swollen at the ends, 4.5-6 x 1.5-1.8 µm; Spot tests: all negative; Secondary metabolites: nonse detected.; Substrate and ecology: often on calciferous soil, also; World distribution: North America, Iceland, Europe, northern Africa, Near and Middle East, India, and New Zealand; Sonoran distribution: quite common in Arizona, also southern California, Baja California, Baja California Sur, and Sonora.; Notes: Collema crispum is distinguished by its numerous scale-like isidia resembling small lobules and its often ear-shaped, overlapping, flat to concave lobes. Rarely, the lobes and/or apothecial discs are pruinose.